DC to DC converter systems are typically used to supply the electrical power requirements of electronic equipment. The converter systems receive electrical energy from a primary DC source and provide electrical energy output at a precisely controlled voltage or current magnitude. The primary DC source is typically an unregulated voltage source such as a full wave rectifier having a filtered output and an input connected to utility AC power or alternatively the output of an uninterruptible power supply.
DC to DC converters are typically used in applications such as electronic equipment where there is a requirement for one or more regulated voltages, overload protection in the form of current limiting to guard against a short circuit, and galvanic isolation of relatively low voltage loads from higher voltage primary power sources. There are oftentimes requirements for synchronization of the converter switching frequency to an external clock signal and for a bidirectional current sharing signal that enables multiple converters to be connected in parallel so they can share a common load. A continuing trend toward circuit miniaturization demands ever smaller sizes while power conversion efficiency, low cost and reliability remain extremely important.
Conventional DC to DC converters use analog feedback loops that must be custom designed to meet specific requirements for primary input voltage, output voltage and output current. Such designs tend to be relatively inflexible. The design costs are difficult to justify unless a large number of units are to be manufactured. Furthermore, manufacturing costs are often increased by a need to custom select and fit certain circuit components during production testing.
U.S. Pat. No. 6,169,669 to Choudhury teaches an uninterruptible power supply that uses a digital signal processor to control conversion of AC power to DC power and back to AC power. In the event of a power failure, the output AC power is generated in response to DC power provided by a backup battery. U.S. Pat. No. 6,031,749 to Covington et al. teaches a universal power module for lighting systems in which a power converter controlled by a digital signal processor converts a high voltage AC input to DC and then controls power output transistors to generate a desired power output characteristic.
However, a need remains for a flexible, high efficiency, reliable and low cost DC to DC converter that can be readily adapted to accommodate smaller production runs having varying requirements for input voltage, output voltage and current limits.
An accurate, low cost, flexible DC to DC converter system and method in accordance with the invention includes a plurality of DC to DC converter units connected in parallel, a pulse width modulation current share bus interconnecting the DC to DC converter units, and a synchronization source providing a synchronization signal to each of the DC to DC converter units. Mutual pulse width modulation communication of DC to DC converter unit current information over the current share bus facilitates resolution of master/slave contention among the DC to DC converter units while enabling substantially equal current sharing and accommodation of a DC to DC converter unit drop out.
A method in accordance with the invention includes generating a synchronization signal, synchronizing the clock signals of a plurality of DC to DC converter units to the synchronization signal, generating on the current share bus a pulse width modulation current share signal by each DC to DC converter unit, resolving master/slave contention at each DC to DC converter unit in response to the pulse width modulation signals appearing on the current share bus, automatically assuming the current load of a failed DC to DC converter unit among the other DC to DC converter units and providing substantially equal load current from each operating DC to DC converter unit.
Each DC to DC converter unit includes a power section having two power converter circuits that operate in response to two pulse width modulated power switch control signals, a controller and a standardized universal interface providing communication between the controller and the power section. Communication of signals through the universal interface at standardized signal levels enables changes in the power section to be made to accommodate different input voltages, output voltages and load currents without requiring significant hardware changes in the controller. The standardized universal interface signals include power signals for operation of the controller, signals representing power section input voltage, output voltage and current as well as pulse width modulation power switch control signals controlling the operation of the power section. The power section includes two power converter circuits that are operated in either single converter or dual converter mode at either regular or double frequency in response to pulse width modulation power switch control signals as necessary to maintain required output current while operating in continuous current conduction mode when possible.
Each controller includes a digital data processor communicating the pulse width modulation power switch control signals through the standardized universal interface in response to the power signals, current signals, and input and output voltage signals received from the power section through the standardized universal interface. The digital signal processor reads and drives the current share bus and responds to current share information by either assuming master status and regulating system output voltage or assuming slave status by driving the output with a current substantially equal the current provided by the master. The digital signal processor preferably stores a calibration table that matches the control program to the particular component and operating characteristics of the DC to DC converter unit.